There are hundreds of craniofacial diseases in humans and cleft palate is common among these. The goal of this proposal is to elucidate the signaling interactions and cellular behaviors underlying palatogenesis. The zebrafish provides a useful model system in which to study palatal development. Powerful genetic and cellular techniques are available in the zebrafish for studying gene function as well as cell and tissue signaling interactions. Additionally, the simplified palatal skeleton, consisting of far fewer neural crest palate progenitors than in mammals, and the optic clarity of the zebrafish embryo makes it ideal for analyzing cell behaviors occurring in palatogenesis. I propose to examine predictions of a reciprocal signaling hypothesis, in which signals from neural crest to the oral ectoderm and then back from the oral ectoderm to neural crest induce palatogenesis, and cause elongation of the palate through cell intercalations. In Specific Aim 1,1 examine the role of candidate genes for neural crest-derived signals and oral ectoderm response genes, turned on in the oral ectoderm. I use loss-of-function, gene expression, imaging, and genetic mosaic analyses to test the model that FgflO and Bmp4 signaling from the neural crest turns on pitx2 in the oral ectoderm, which, in turn, promotes palatogenesis. In Specific Aim 2,1 analyze the reciprocal signal, from oral ectoderm to neural crest. I use loss-of-function, imaging, and genetic mosaic analyses as well as construction of inducible transgenic zebrafish lines to test the prediction that Pdgf and Eph/ephrin signaling from the oral ectoderm promotes palatogenesis. In Specific Aim 3,1 determine the cell behaviors that drive elongation of the palate. I use confocal time lapse analysis as well as cloning and characterization of novel zebrafish palate mutants to test the prediction that cell intercalations drive the extension of the zebrafish palate. The results I obtain during the course of these studies will shed light on the genetic and cellular causes of cleft palate. Additionally, two genes I propose to analyze, pitx2 and ephrin-B1, are known to be human craniofacial disease genes. Therefore, my analyses of these genes will provide direct insight into the cause of human disease.